Radar system to suppress interference signals



Jan. 26, 1965 G. LE PARQUIER RADAR SYSTEM TO SUPPRESS INTERFERENCE SIGNALS Filed Oct. 4, 1961 4 Sheets-Sheet 2 l5 17 Transm/ter n- Dupexev Attenuator i Ampllf/cr Y Attenuaor Phase .fh/fr /Jmplrfler Phase Shifter Fl G. 2 Qing Cir-cult 554 154 26 025 FIC-'2.5

Jam 26, 1965 G. LE PARQUlr-:R 3,167,761

RADAR SYSTEM TO SUPPRESS INTERFEREINCE SIGNALS Filed Oct. 4, 1961 4 Sheets-Sheet 3 Transmllfer Dup/exer D'rccu'pO/g/ A Tranfml/Ier fenuator 54 PhaseShlfter Coup/lng /25 Circuit 55'1 54 26; 425

FIG. 52 52 5 Coup/lng 65 Circuit /16 f7 V65 L6 /64 Transmitter Uup/exer T-R Tu be FIG.4

Jan. 26, 1965 G. LE PARQUIER 3,167,761

RADAR SYSTEM To sUPPREss INTERFERENCE sIGNALs 4 Sheets-Sheet 4 Filed 0G17. 4. 1961 translation to an intermediate frequency and amplification, the sum signal and the difference signal n=1,12=a sin (wars) are respectively collected atv the outputs 5 and 6 of the ampliers 27 and 28: Il and I2 Corresponding to the output signals of the main and of the auxiliary channels, respectively.

At the outputs of the phase and amplitude detectors 29 and 39, there are collected the signals A=ksd cos (l-7) and B=k s d sin (6 6), where k is a constant.

These two signals are applied to a distributor 32 which, in the example described, delivers to the control inputs of attenuator 21 and phase-shifter 22 respectively two error signals which, within given constant factors depending upon the gain of the feed-back loop, are of the form p=sd and H=- r, respectively, -a being expressed by a variable polarity signal. These signals have besides been subjected to the indicated frequency band limitation.

' Signals p and 0 are respectively applied to attenuator 2l and phase-shifter 22, in the proper direction, i.e. so that through the action of the servo-system the difference between the amplitudes of l1 and I2 and the difference between the phases of I1 and I2 tend towards zero, the

cih

for locating the radar station and a jammer covering the same frequency band, and it is desired to operate both the radar and the jammer simultaneously, i.e. to operate the radar without affecting its operation by ones own jammer operation.

This arrangement is similar to that shown in FIG. l, except that the jammer transmitter 52 is substituted for the auxiliary aerial 2 and that the variable phase-shifter and attenuator are inserted in the auxiliary channel, instead of the main channel. A directional coupler 50 is inserted between aerial 5I of the jammer unit and the transmitter 52 thereof. This directional coupler feeds,

Vthrough one of its outputs, an attenuator 53, followed by a phase-shifter Sil, the output of which is coupled to one of the inputs of the coupling circuit 23, the other input of the coupling circuit 23 being coupled directly to the duplexer i7. rl`he control signals derived from distributor 52 are applied to the control inputs of attenuator 53 and phase-shifter 54, respectively.

The systems described hereinabove make it possible to detect readily a target, the direction of which, as seen Vfrom the radar, differs sufciently from that of the jamf mer or another source ot interference signals so that the system assuming its rest position only when these conditions are satistied with an approximation depending upon the gain of the feed-back loop.

Under these conditions, the servosystern, in the presence of interference signals, lfor example from a jammer, tends to control the diiference signal detected by detector 15. But if an echo pulse is picked up by the main aerial, the resulting error signal, dueto the limitation of the error signal frequency band, cannotniodify the adjustment of attenuator 2l` and phase-shifter 22 as indicated above, and the difference signal thus collected at the output 6 is detected at 15 and may be used for indicating or other purposes.

For the operation ofthe receiver illustrated in the block diagram of FIG. 1, it is assumed that the interference signals picked up by the Imain aerial have a higher energy level than the same signals received by the auxiliary aerial, which condition may be generally satisiied by conveniently selecting the gain of the auxiliary aerial.

It is however possible to overcome this limitation by using a phase shifter and an attenuator in each of the channels preceding the addition and subtraction circuit. This alternative is illustrated in FIG. 2, where the components of the circuit preceding the coupling circuit 23 are illustrated with the addition of a variable attenuator il and a variable phase-shifter42 connected in series between the auxiliary aerial 2 and the coupling circuit 23, and of two ampliliers 43 and 44, each of which'has two outputs respectively delivering signals varying in opposite directions. The two outputs of amplifier i3 are respectively connected to the control inputs of the attenuators 21 and 41 and the two outputs of amplier 44 are respectively connected to the control inputs of the phase-Shifters 22 and 42. The output signals p and 0 of distributor 32 are applied to the inputsV of ampliers 43, 44 and no longer directly to attenuatorZll and phase-shifter 22. VTheV remainder of the circuit remains unmodified relative to FIG. l.

The signals delivered by the distributor 32 are of the same'form as indicated hereinabove. The output signals of amplifiers i3 and 44 are applied to the attenuators and to the phase-ShiftersV so that the attenuation increases in creases in the other, and viceversa.

FIG. 3 is an alternative embodiment of the arrange-V ment according to the invention, when a vehicle is used amplitude and phase adjustment effected for the direction of the jammer are not also effective in the direction of the target.

In other words, the detection of the useful targets is very dir'licult or even impossible, when they vare located in a direction such that the source of interference signals is located in the axial zone of the main lobe of the main aerial, when the axis of this lobe is directed towards the target. i

This does ynot hold true, if instead of arsubstantially omnidirectional auxiliary aerial, an auxiliary aerial isused, the radiating pattern of which presents a very sharp split in a given direction and if this auxiliary aerial is caused to rotate in synchronism with the rnain aerial, so that the axis of this split coincides with that of the main lobe of the main aerial. Under these conditions, the diferential gain between the two patterns varies very rapidly in the neighborhood of the radioelectric axis of the aerial. This enables to eliminate the signals coming from jammers, Without affecting the signals coming from targets lying very'nearly in the same direction.

Instead of such an aerial system, anV equivalent system maybe provided wherein the sum and diierence signals of a monopulse radar aerial are used, instead of the signals delivered, as in the previously described embodiments, by the main andauxiliary aerials respectively.

FIG. 5 represents both, in decibels, radiating patterns g and d o a monopulse aerial, viz. the left-hand andthe right-hand beams. f

In FIG. 6, `there is shown, also in db, the sum pattern p and the dil-ference pattern a which presents a very sharp split in the direction of the maximum of pattern p.

Monopulse aerial systems comprising two aerial portions and a coupling elenientrsup'plying the'surnv and theV dierence of the signals supplied by the two portions are well known andvdescribed for example in Introduction to l Monopulse by Donald R. Rhodes, McGraw-Hill Book Co. A monopulse aerial of the aforesaid type is, for example, shown in FIG.V 1.9 on page 18 of this'work.

, vFIG. 4 illustrates another-modification of the system according tothe invention, which diiers from thediagram in lFIGQZ only by the elements preceding the rattenuators 21 and41.. l

VBoth portions 6l and 62 of fa monopulse aerial, correspending -to the radiating patterns g Aand d of FIG. 5, feed `a coupling .circuit 63 delivering on itsl outputs 65 and 65 respectively the sum Y'and difference signals of the input signals. The output 65 feeds, through Vduplexer I7, `attenuator 2i and the output 66, through la protecting Tltube Y Y tion and subtraction circuit, said feedback loop comprising low pass iiltering means.

5. ln a radar system comprising an aerial system of the monopulse type, said aerial system comprising two aerial portions, and -a coupling circuit having a sum output and a d-herence output, said sum output supplying signals corresponding to a sum radiation pattern :and said dierence output supplying signals corresponding to a difference radiation pattern, and a transmitter feeding said aerial portions to transmit a beam according to said sum radiation pattern, a receiver comprising: a main channel fed by said sum output of said aerial and comprising a rst variable attenuator and a first variable phase-shifter Vhaving respective control inputs; an auxiliary input channel fed by said ydifference output 'of said aerial Vand comprising a second variable attenuator and a second variable ph-aseshifter having respective control inputs; a first amplifier, having a control input, for delivering two signals, varying in `opposite directions, on two outputs `respectively coupled to said control inputs of said first and second variable attenuators; a second ampliiier, having a control input, for delivering signals, varying in opposite directions,

von two outputs respectively coupled to said control inputs of said first and second variable phase-Shifters; an

addition and subtraction circuit having two inputs respectively fed by said two input channels and two outputs feeding respectively a sum channel with a snm signal and a difference channel with a difference signal; means coupled to said diierence channel for detecting said difference signal; means coupled to :said sum channel and to said difference channel for deriving from said sum signal and from said difference sign-al a rst error signal tending towards zero when the amplitude of said difference signal tends towards zero and a second ernor signal tending towards zero when the phasefshift between said sum signal and said difference signal tends towards zero and for upwardly, limiting the frequency band of said error signals; and means for applying said tirst error signal to said control input of ysaid first amplifier and said second error signal to said control input of said second amplifier,

References Cited by the Examiner UNITED STATES PATENTS CHESTER L. J USTUS, Primary Examiner. 

1. A RADAR RECEIVER COMPRISING: A RADAR TRANSMITTINGRECEIVING AERIAL; A MAIN INPUT CHANNEL FED BY THE RADAR TRANSMITTING-RECEIVING AERIAL; AN AUXILIARY SUBSTANTIALLY OMNIDIRECTIONAL AERIAL; AN AUXILIARLY INPUT CHANNEL FED BY SAID AUXILIARY AERIAL; A VARIABLE ATTENUATOR, HAVING A CONTROL INPUT, INSERTED IN ONE OF SAID INPUT CHANNELS; A VARIABLE PHASE-SHIFTER, HAVING A CONTROL INPUT, INSERTED IN ONE OF SAID INPUT CHANNELS; AN ADDITION AND SUBTRACTION CIRCUIT HAVING TWO INPUTS RESPECTIVELY FED BY SAID TWO INPUT CHANNELS AND TWO OUTPUTS FEEDING RESPECTIVELY A SUM CHANNEL WITH A SUM SIGNAL AND A DIFFERENCE CHANNEL WITH A DIFFERENCE SIGNAL; MEANS COUPLED TO SAID DIFFERENCE CHANNEL FOR DETECTING SAID DIFFERENCE SIGNAL; MEANS COUPLED TO SAID SUM CHANNEL AND TO SAID DIFFERENCE CHANNEL FOR DERIVING FROM SAID SUM SIGNAL AND FROM SAID DIFFERENCE SIGNAL A FIRST ERROR SIGNAL TENDING TOWARD ZERO WHEN THE AMPLITUDE OF SAID DIFFERENCE SIGNAL TENDS TOWARDS ZERO AND A SECOND ERROR SIGNAL TENDING TOWARD ZERO WHEN THE PHASE-SHIFT BETWEEN SAID SUM SIGNAL AND SAID DIFFERENCE SIGNAL TENDS TOWARDS ZERO AND FOR UPWARDLY LIMITING THE FREQUENCY BAND OF SAID ERROR SIGNALS; AND MEANS FOR APPLYING SAID FIRST ERROR SIGNAL TO SAID CONTROL INPUT OF SAID VARIABLE ATTENUATOR AND SAID SECOND ERROR SIGNAL TO SAID CONTROL INPUT OF SAID VARIABLE PHASE-SHIFTER. 